The women’s boxing match at the Olympic Games in Paris has highlighted how complex the development and enforcement of gender-specific participation rules in women’s sport is and how vulnerable athletes such as Algeria’s Imane Khelif and Taiwan’s Lin Yu-ting are to the consequences.

When the eligibility of women to compete was questioned, it was often a legally difficult process for sports governing bodies that could expose athletes to humiliation and abuse. In the 1960s, the Olympic Games used degrading visual tests to verify the gender of athletes.

The modern era of eligibility famously began in 2009, after South African 800-meter runner Caster Semenya rose to athletics stardom as an 18-year-old gold medalist at the World Championships.

Semenya, an Olympic 800-meter champion in 2012 and 2016, will not compete in Paris because she is effectively banned from competing unless she medically lowers her testosterone levels. But she is still embroiled in a lawsuit against athletics rules that is now in its seventh year.

Here’s a look at gender testing in sport and the complexity it creates in the face of changing attitudes towards gender identity:

What are the criteria for women to participate?

Testosterone levels – not XY chromosomes, the typical pattern in men – are the most important criterion for participation in Olympic competitions, for which the sport’s governing body has established and approved rules.

That’s because some women who were assigned female at birth and identify as women have a disorder called differences in sex development (DSD), which is an XY chromosome pattern or natural testosterone levels that are higher than the typical female range. Some sports officials say this gives them an unfair advantage over other women in sports, but the science disagrees.

Semenya, whose medical information could not be kept secret during her legal proceedings, suffers from DSD. She was legally identified as female at birth and has identified as female throughout her life.

Testosterone is a natural hormone that increases the mass and strength of bones and muscles after puberty. The normal range in adult men rises several times higher than in women, up to about 30 nanomoles per liter of blood compared to less than 2 nmol/L in women.

At a hearing before the Court of Arbitration for Sport in 2019, the athletics governing body argued that athletes with DSD conditions were “biologically male.” Semenya said this was “deeply hurtful.”

Semenya’s case played out very publicly before 2021, when gender identity was a big issue at the Tokyo Olympics and in society and sport in general. She took oral contraceptives from 2010 to 2015 to lower her testosterone levels and said these caused a variety of unwanted side effects: weight gain, fever, a constant feeling of nausea and abdominal pain, all of which she experienced while running at the 2011 World Championships and the 2012 Olympics.

Female athletes of color have historically faced disproportionate scrutiny and discrimination when it comes to gender testing and false accusations that they are male or transgender.

Why do gender verification tests differ for different sports?

Each governing body of an Olympic sport is responsible for developing its own rules, from the field of play to eligibility.

Women’s boxing came to the Paris Games with virtually the same entry criteria – an athlete must be female on her passport – as it did at the 2016 Olympics in Rio de Janeiro, after the International Boxing Federation was permanently banned from the Games following decades of crisis-ridden leadership and long-standing accusations of a complete lack of normal transparency. Much has happened in the science and debate in those eight years.

Since the 2021 Olympic Games in Tokyo, the World Athletics Association has tightened the participation requirements for athletes with DSD. From March 2023, they will have to reduce their testosterone levels below 2.5 nmol/l for six months, usually through hormone-suppressing treatment, in order to be able to compete.

This was half the value of 5 nmol/L proposed in 2015 for athletes running distances between 400 meters and 1 mile (1.6 kilometers).

The International Athletics Federation followed the example of another major sport – the World Aquatics Federation – and banned transgender women from participating in women’s races once they have gone through male puberty. The International Cycling Federation also took the same step last year.

The world-leading swimming association’s rules also require transgender athletes who have not benefited from male puberty to have a testosterone level below 2.5 nmol/l.

World Aquatics does not actively test junior athletes. The first step for athletes is for national swimming federations to “certify their chromosomal sex.”

FIFA, the world football association, also leaves it up to its national member associations to check and register the gender of players.

“There will be no mandatory or routine gender verification examinations at FIFA competitions,” said a 2011 recommendation that is still valid and has undergone a lengthy review.

Why is it important for boards to know who identifies as a woman?

Many sports associations try to balance inclusion of all athletes with fairness for everyone on the field. They also argue that in contact and combat sports such as boxing, physical safety is an important consideration.

In the Semenya case, the judges of the Court of Arbitration for Sport recognised in a 2-1 ruling against her that discrimination against some women was “a necessary, reasonable and proportionate means” of maintaining fairness.

Male athletes do not need to regulate their natural testosterone levels and female athletes who do not suffer from DSD can also benefit.

“The idea that a testosterone test is some kind of miracle cure is actually not true,” said Mark Adams, spokesman for the International Olympic Committee, in Paris, as the debate over women’s boxing sparked heated debates.

What does the IOC require?

Sometimes the IOC has a lot of power, but sometimes it has none at all.

The Switzerland-based organization administers the Olympic Charter, owns the Olympic brand, selects the hosts and supports their financing through the billions of dollars it earns from the sale of broadcast and sponsorship rights.

However, Olympic sporting events are governed by individual governing bodies such as FIFA and World Athletics, which codify and enforce their own rules governing athlete eligibility, the field of play and disciplinary regulations.

As Olympic sports reviewed and updated their approach to gender issues, including with respect to transgender athletes, the IOC published recommendations in 2021, but no binding rules.

This was the organization’s framework for gender and sexual inclusion, which recognized the need for a “safe, harassment-free environment” that honored athletes’ identities while ensuring fair competition.

In boxing, however, the situation was different and the consequences were harsh in Paris.

For years, the IOC has been involved in an increasingly bitter dispute with the International Boxing Federation, which is now led by Russia. The dispute culminated last year in a permanent exclusion from the Olympic Games.

For the second year in a row, the Summer Olympics in boxing were governed by an administrative committee appointed by the IOC rather than by a functioning governing body.

In this respect, boxing’s eligibility requirements have not kept pace with those in other sports and the issues were not addressed in the run-up to the Paris Games.

At the 2023 World Championships, Khelif and Lin were disqualified by the IBA and did not receive medals. The IBA said they had failed the eligibility tests for the women’s competition but released little information about them. The governing body repeatedly contradicted itself on whether the tests measured testosterone.

In a chaotic press conference in Paris on Monday, IBA officials said they had conducted blood tests on only four of the hundreds of fighters at the 2022 world championships and that the tests on Khelif and Lin were done in response to complaints from other teams, apparently acknowledging an inconsistent standard of profiling that is widely considered unacceptable in the sport.

Who questions established rules in some sports?

Before Semenya, it was Indian sprinter Dutee Chand who appealed to the International Court of Arbitration for Sport (ICAC), challenging athletics’ original testosterone rules, which were introduced in 2011 in response to Semenya.

An initial CAS ruling for Chand in 2015 froze the rules and led to an update in 2018, which was then challenged by Semenya, whose 800m career stalled because she refused to take drugs to artificially suppress her testosterone levels and was banned from competing in elite events.

Semenya lost at CAS in 2019 but appealed via Switzerland’s Supreme Court to the European Court of Human Rights, where she won a landmark, if not complete, victory last year.

Another hearing in the Semenya case took place before the ECHR in May; a verdict is expected next year.

The case could be sent back to Switzerland, perhaps even to the CAS in the Olympic hometown of Lausanne. Other sports are watching and waiting.